Species [ var. minutum ]: Cell body cylindrical, 50-230 μm long, 7-18 μm wide, L/W=8-12; semicells not swelled at base, slightly tapered, with blunt and smooth ends; cell wall smooth or finely dotted; chloroplasts located along cenral axis, with about 6 laminae; pyrenoids arranged linearly, 3-7 in each semicells. [ var. elongatum (W. et G.S. West) Cedergren ]: 257-550 μm long, 8-16 μm wide, L/W=28-40; [ var. crassum (W. West) Krieger ]: Shorter and wider than v. minutum, 40-102 μm long, 12-20 μm wide, L/W=4-5; [ var. cylindricum (Borge) Krieger ]: 175-300 μm long, 15.5-21 μm wide, L/W=14-15; [ var. gracile (Wille) Krieger ]: Thinner and longer than v. minutum, 110-240 μm long, 6.5-15 μm wide, L/W=14-20; [ var. latum Kaiser ]: Wider than v. minutum, 160-352 μm long, 19-28 μm wide, L/W=8-11 (Illustrations of The Japanese Fresh-water Algae, 1977).

50 μm 100 μm 150 μm; x 400

31 μm 63 μm 94 μm; x 640